The present invention relates to an image processing apparatus, an image processing method, and a recording medium which are suitable for synthesizing a hair image expressed by computer graphics with a three-dimensional shape image of a head part.
Conventionally, as a method for expressing human hair by computer graphics (hereinafter abbreviated as CG), it is useful to take a method in which an entire hair style is approximated to a polygon model, as shown in FIG. 1A, and a texture of hairs is adhered to the model, or a method in which rendering is performed with use of an anisotropic reflection model which has different reflection intensities respectively with respect to light source positions or viewpoint positions.
These methods are described in “Hair expression using an anisotropic reflection model” by Yamana and Suenaga, Singakugihou, PRU87-3, pp. 115 to 120, 1989. In these methods, expression of a hair style is just the shape of a polygon model itself, and the hair style can be changed by changing the shape of the polygon model.
A proposal has been made for a method of expressing hair by a particle system. In the particle system, when a large quantity of particle objects are dealt with, characteristics such as weight and the like of each particle are given as parameters, and particles are generated under a certain rule. Thus, a large quantity of particle objects can be expressed easily.
Meanwhile, the present applicant has proposed a method of approximating every hair of a hair-style to a curve, as shown in FIG. 1B, in Japanese Patent Application No. 10-164545, for example. This method is successful in natural expression of a hair style image.
A method of designing a hair style by editing together a plurality of hairs approximated to a curve is described in “Development of a hair design system using tuft models” by Kishi, Saegusa, and Morishima, in Shingakugihou, MVE97-102, pp. 67-74, 1998.
It is difficult for the method of approximating the entire hair style to a polygon model to express a complicated hair style. In this method, movements (flows) of hair cannot be expressed.
On the other side, the method of expressing hair by a particle system and the method of approximating every hair to a geometric figure can express any arbitrary hair style and movements of hair. However, in the method of expressing hair by the particle system, parameters for particles expressing hairs must be controlled to control the hair style, so that intuitive control is difficult. It is therefore difficult to generate an intended hair style.
In the method described in “Development of a hair design system using tuft models” by Kishi, Saegusa, and Morishima, in Shingakugihou, MVE97-102, pp. 67-74, 1998, an intended hair style can be generated relatively easily. This method, however, has a problem in that hair cannot be changed to intended hair styles corresponding to a plurality of different head shapes although hair corresponding only to one fixed head shape can be changed to an intended hair style.